Reverse link initial power setting using effective radiated power message to compute path loss

ABSTRACT

In an illustrative embodiment of the present invention, a reference signal including pilot information is transmitted from a base station to one or multiple field units over a pilot channel. A message is also sent to the field units over a paging channel to indicate an effective radiated power level at which the reference signal is transmitted on the pilot channel. Based on a received power level of the reference signal at a field unit and the effective radiated power level of the reference signal, a forward path loss is estimated at the field unit for the forward link between the base station and field unit. Assuming the path loss in the reverse link is approximately the same as the estimated forward link path loss, the field unit can transmit, a reply message in the reverse link so that the base station generally receives a message at-a desired power level.

RELATED APPLICATION(S)

[0001] This application is a continuation application of U.S.application Ser. No. 09/792,870 filed on Feb. 23, 2001 which claims thebenefit of U.S. Provisional Application No. 60/184,223 filed on Feb. 23,2000, the entire teachings of which is incorporated herein by thisreference.

BACKGROUND OF THE INVENTION

[0002] A specific protocol has been developed for allowing multipleusers to transmit over a shared radio channel. For example, the IEEE(Institute of Electrical and Electronics Engineers) 802.11 Standardgenerally supports access to radio channels based on a method known asCarrier Sense Multiple Access with Collision Avoidance (CSMA/CA).

[0003] In simple terms, this method is based on a “listen before talk”scheme. A transmitter device monitors traffic on a shared radio channelto determine if another transmitter device is presently transmitting onthe same channel. If the radio channel is in use, the transmitter devicewill continue to monitor the channel until it is clear. When the radiochannel is finally clear, the transmitter will then transmit over theradio channel.

[0004] Ideally, another transmitter device will not simultaneouslytransmit during the same time. However, a collision can occur on theradio channel when two or more transmitter devices transmit on the radiochannel simultaneously. Consequently, neither message transmission wouldbe intelligible and both transmitter devices must re-transmit theirmessages again to a corresponding target device.

[0005] Based on this CSMA/CA scheme, re-transmission of data due to acollision cannot occur before a minimum time gap. After the minimum timegap has passed, the transmitter device selects a random “backoffinterval,” which is the wait time before the radio channel is againmonitored to determine whether the radio channel is clear to transmit.If the channel is still busy, another shorter “backoff interval,” isselected for a subsequent message transmission. This process is repeateduntil the transmitter device is able to transmit data.

[0006] Another standard for transmitting data on a shared radio channelis based on IS-95, in which multiple field units can transmit at thesame time.

[0007] The IS-95 standard suggests a method of ramping RF power of afield unit until a message from the field unit is transmitted at a powerlevel that is detectable at a base station. According to this method, afield unit transmits an access request message to a base station for theassignment of wireless resources on a reverse link.

[0008] After transmitting an access request message on an accesschannel, the field unit monitors a paging channel for an acknowledgmentmessage from the base station indicating that the access request messagewas properly received. If no acknowledgment message is sent to therequesting field unit, it is presumed that the message from the fieldunit was not transmitted at an appropriate power level. That is, thepower output level of the field unit is so low that the base station didnot detect a previously transmitted access request message. The accessrequest message is then re-transmitted over the access channel at ahigher power level.

[0009] This process is subsequently repeated until the field unittransmits a message at a power level that is high enough for the basestation to properly receive the message. Similar to the IEEE 802.11standard, a collision can occur on the shared radio channel when two ormore field units simultaneously transmit a message.

SUMMARY OF THE INVENTION

[0010] The present invention is generally directed towards an apparatusand method for enhancing the utilization of resources in a wirelesscommunication system. In an illustrative embodiment, a reference signalis transmitted from a first transceiver to a second transceiver or groupof target transceivers. The first transceiver also transmits a firstmessage, which includes information indicating an effective radiatedpower level at which the first transceiver transmits the referencesignal. The received power level of the reference signal is thenmeasured at the second transceiver to estimate a path loss between thefirst transceiver and second transceiver. More specifically, a path losscan be calculated by comparing the received power level of the referencesignal with the effective radiated power level information as indicatedby the first message.

[0011] A second message is optionally sent from the first transceiver tothe second transceiver. This second message can include informationindicating a desired power level at which subsequent messages in areverse direction should be received at the first transceiver.

[0012] In certain applications, the forward path loss between the firsttransceiver and second transceiver is approximately the same as areverse path loss for message transmissions from the second transceiverback to the first transceiver. Consequently, the second transceiver canadjust its power output level so that the first transceiver receives amessage at the desired power level taking into account the estimatedpath loss as previously discussed. Of course, the path loss can bedifferent in the reverse link direction than that of the forward linkand an estimated power setting at which the second transceiver transmitsa message can be a starting point for transmitting subsequent messages.For example, the power output level of the second transceiver can beincreased for subsequent message transmissions until the firsttransceiver detects the message.

[0013] In a specific application of the present invention, the referencesignal is transmitted over a pilot channel of a CDMA (Code DivisionMultiple Access) communication system. The reference signal itselfoptionally includes a marker such as pilot symbols that are monitored ata second transceiver. The first message as transmitted by the firsttransceiver can be transmitted over a paging channel, while a replymessage from the second transceiver to the first transceiver can betransmitted over an access channel in which multiple transceiverscompete to transmit messages to the first transceiver. The accesschannel is optionally divided into time slots in which a transceiversends a message to the first transceiver.

[0014] One message type that can be transmitted on the access channel isan access request message. Such a message is an indication to the firsttransceiver that a more formal communication link should be establishedbetween the first transceiver and second transceiver. Consequently, themore formal communication link can be allocated to support moreefficient, on-demand data transfers.

[0015] An access request message is optionally encoded so that itincludes timing alignment information. For example, the firsttransceiver can analyze a reply message such as an access requestmessage including a timing marker and provide feedback indicatingwhether the reply is appropriately transmitted within a time slot. Othertypes of reply messages can also include a reference marker for timingalignment. In one application, a reference marker is a string includingpilot information such as one or multiple pilot symbols.

[0016] In addition to monitoring the timing of a reply message, thereceived power level of a reply message can be monitored to determinewhether a transceiver is transmitting a message so that it is receivedat a desired power level. This can be achieved by comparing a powerlevel at which a reply message is received to a desired power level atwhich the reply message should be received. Based on this comparison, apower adjustment message is optionally transmitted to a correspondingtarget transceiver. Thus, subsequent message transmissions from a secondtransceiver to the first transceiver can be optimally adjusted based onoperating conditions of the wireless communication system at an instantin time.

[0017] Certain aspects of the present invention reduce co-channelinterference and generally increase the throughput capability of awireless communication system. As previously discussed, an initial poweroutput level of a field unit can be adjusted so that it minimallyinterferes with others when it initially transmits messages or transmitssubsequent messages. When message transmissions on an allocated channelsuch as an access channel are minimized, more wireless resources canotherwise be allocated for supporting higher speed data transfers in awireless communication system.

[0018] Of course, the initial power output level of a field unit can beso low that a message transmission is not detected at a target devicesuch as a base station. In this case, a power output level can beincreased accordingly for subsequent message transmissions until themessage is detected at a target transceiver. This process ofincrementally increasing the power level can be a time consumingprocess, especially if the power output of the transceiver were to starttransmitting at a lowest possible power level. Thus, it can take aconsiderable amount of time to successfully transmit a message to atarget receiver such as a base station.

[0019] The principles of the present invention can be used tosimultaneously reduce the effective time it takes to transmit a messageto a base station while minimally interfering with other channels of thewireless communication system. This is achieved, at least in part, byapproximating a path loss between a field unit and base station andtransmitting a message from the field unit so that a message is receivedat a desired power level at the base station. Since the initial powersetting of the field unit is approximately set to a detectable powerlevel for data transmissions to a target receiver, it typically requiresless time to transmit an initial message to a target receiver when poweris incrementally increased so that a message is eventually detected.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a bock diagram of an illustrative wireless communicationsystem according to certain principles of the present invention.

[0021]FIG. 2 is a timing diagram illustrating multiple channels on whichmessages are transmitted according to certain principles of the presentinvention.

[0022]FIG. 3 is a timing diagram illustrating a use of data fieldswithin a time-slotted channel according to certain principles of thepresent invention.

[0023]FIG. 4 is a pictorial diagram illustrating details of a messageaccording to certain principles of the present invention.

[0024]FIG. 5 is a flow chart for processing messages at a targetreceiver according to certain principles of the present invention.

[0025]FIG. 6 is a flow chart for transmitting messages to a targetreceiver according to certain principles of the present invention.

[0026]FIG. 7 is a timing diagram illustrating multiple channels on whichmessages are transmitted according to certain principles of the presentinvention.

[0027]FIG. 8 is a diagram of a monitored reference signal according tocertain principles of the present invention.

[0028]FIG. 9 is a flow chart for setting an initial power output levelof a transmitter device according to certain principles of the presentinvention.

[0029] The foregoing and other objects, features and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention, as illustrated inthe accompanying drawings in which like reference characters refer tothe same parts throughout the different views. The drawings are notnecessarily to scale, emphasis instead being placed upon illustratingthe principles of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0030] A description of preferred embodiments of the invention follows.

[0031]FIG. 1 is a block diagram illustrating a wireless communicationsystem supporting the transmission of data information over multipleallocated communication channels according to certain aspects of thepresent invention. As in many wireless communication systems, userscompete for wireless bandwidth allocation. Hence, it is desirable thatthe wireless communication 10 is optimized for data throughput and, incertain applications, hi-speed bursts of data throughput.

[0032] Certain aspects of the present invention are based on therecognition that the power output of a field unit transmitting over awireless channel can be controlled so that it minimally interferes withother field units using the same general wireless airspace. Inparticular, a power output level of a newly transmitting field unit isinitially set so low that a base station may not detect messagestransmitted by the field unit. This initially low power setting of afield unit reduces co-channel interference because the transmitterdevice is not transmitting at excessive power levels. During subsequentcommunication attempts with the base station, the power output of afield unit is then ramped up until messages are acknowledged at the basestation.

[0033] In one application, one or multiple field units randomly transmitmessages on a first allocated channel. When two field units transmit amessage simultaneously on this first allocated channel, there can be amessage collision at the base station. The base station may be able todetect that a message was transmitted by a field unit and there was amessage collision. However, the base station may not be able to decipherthe contents of the message and determine from which field unittransmitted a message. Thus, in certain situations, the base station cannot transmit a message directed specifically to a particular field unitindicating that a collision occurred for a previous messagetransmission.

[0034] One aspect of the present invention involves providing generalfeedback information to the field units indicating that a collision wasdetected. Consequently, a previous undetected message can bere-transmitted by a field unit. If there was no collision detected andno acknowledgment received by the filed unit, the field unit cansuccessively ramp up its power output setting for subsequent messagetransmission attempts to ensure that a message will eventually beacknowledged by the base station.

[0035] According to the following description of a preferred embodiment,communication system 10 is described as a wireless communication linksuch as a CDMA radio channel utilizing shared channel resources.However, it should be noted that the techniques described herein can beapplied in other applications supporting shared access. For example, theprinciples of the present invention can be applied to other generalapplications such as telephone connections, computer networkconnections, cable connections, or other physical media to whichallocation of resources such as data channels are granted on anas-needed basis.

[0036] As shown, communication system 10 includes a number of PersonalComputer (PC) devices 12-1, 12-2, . . . 12-h, . . . 12-m, correspondingfield units or terminals 14-1, 14-2, . . . 14-h, . . . 14-m, andassociated directional antenna devices 16-1, 16-2, . . . 16-h, 16-m.Centrally located equipment includes a base station antenna 18, and acorresponding base station 20 that includes high speed processingcapability.

[0037] Base station 20 and related infrastructure provides connectionsto and from a network gateway 22, network 24 such as the Internet, andnetwork file server 30. Communication system 10 is preferably a demandaccess, point to multi-point wireless communication system such that thePC devices 12 can transmit data to and receive data from network server30 based on a logical connection including bi-directional wirelessconnections implemented over forward links 40 and reverse links 50. Thatis, in the point to multi-point multiple access wireless communicationsystem 10 as shown, a given base station 20 typically supportscommunication with a number of different field units 14 in a mannerwhich is similar to a cellular telephone communication network.Accordingly, system 10 can provide a framework for a CDMA wirelesscommunication system where digital information is relayed on-demandbetween multiple mobile cellular users and a hardwired network 24 suchas the Internet.

[0038] PC devices 12 are typically laptop computers, handheld units,Internet-enabled cellular telephones, Personal Digital Assistant(PDA)-type computers, digital processors or other end user devices,although almost any type of processing device can be used in place of PCdevices 12. One or multiple PC devices 12 are each connected to arespective subscriber unit 14 through a suitable hard wired connectionsuch as an Ethernet-type connection via cable 13.

[0039] Each field unit 14 permits its associated PC device 12 access tonetwork file server 30. In the reverse link 50 direction, that is, fordata traffic transmitted from the PC 12 towards the server 30, the PCdevice 12 transmits information to field unit 14 based on, for example,an Internet Protocol (IP) level network packets. The field unit 14 thenencapsulates the wired framing, i.e., Ethernet framing, with appropriatewireless connection framing so that data packets can be transmitted overthe wireless link of communication system 10. Based on a selectedwireless protocol, the appropriately formatted wireless data packet thentravels over one of the radio channels that comprise the reverse link 50through field unit antenna 16 to base station antenna 18. At the centralbase station location, the base station 20 then extracts the radio linkframed data packets and reformats the packets into an IP format. Thepackets are then routed through gateway 22 and any number or type ofnetworks 24 to an ultimate destination such as a network file server 30.

[0040] In one application, information generated by PC device 12 isbased on a TCP/IP protocol. Consequently, a PC device 12 has access todigital information such as web pages available on the Internet. Itshould be noted that other types of digital information can betransmitted over channels of communication system 10 based on theprinciples of the present invention.

[0041] Data information can also be transferred from the network fileserver 30 to PCs 12 on forward link 40. In this instance, network datasuch as IP (Internet Protocol) packets originating at file server 30travel on network 24 through gateway 22 to eventually arrive at basestation 20. As previously discussed for reverse link data transmissions,appropriate wireless protocol framing is then added to raw data such asIP packets for communication of the packets over wireless forward link40. The newly framed packets then travel via an RF signal through basestation antenna 18 and field unit antenna 16 to the intended targetfield unit 14. An appropriate target field unit 14 decodes the wirelesspacket protocol layer, and forwards the packet or data packets to theintended PC device 12 that performs further processing such as IP layerprocessing.

[0042] A given PC device 12 and file server 30 can therefore be viewedas the end points of a logical connection at the IP level. Once aconnection is established between the base station processor 20 andcorresponding field unit 14, a user at the PC device 12 can thentransmit data to and receive data from file server 30 on an as-neededbasis.

[0043] Reverse link 50 optionally includes different types of logicaland/or physical radio channels such as an access channel 51, multipletraffic channels 52-1, . . . 52-m, and a maintenance channel 53. Thereverse link access channel 51 is typically used by the subscriber units14 to request an allocation of traffic channels by the base station 20.For example, traffic channels 52 can be assigned to users on anas-needed basis. The assigned traffic channels 52 in the reverse link 50then carry payload data from field unit 14 to base station 20.

[0044] Notably, a given link between base station 20 and field unit 14can have more than one traffic channel 52 assigned to it at a giveninstant in time. This enables the transfer of information at higherrates.

[0045] Maintenance channel 53 can be used to carry maintenanceinformation such as synchronization and power control messages tofurther support transmission of digital information over both reverselink 50 and forward link 40.

[0046] Forward link 40 can include a paging channel 41, which is used bybase station 20 to inform a field unit 14 of general information such asthat one or multiple forward link traffic channels 42 have beenallocated to it for forward link data transmissions. Traffic channels42-1 . . . 42-n on the forward link 40 are used to carry payloadinformation from base station 20 to a corresponding target subscriberunit 14.

[0047] Maintenance channel 43 can be used to transmit synchronizationand power control information on forward link 40 from base stationprocessor 20 to field units 14. Additionally, paging channel 41 can beused to inform a field unit 14 of allocated traffic channels 52 in thereverse link 50 direction.

[0048] Traffic channels 42 of the forward link 40 can be shared amongmultiple subscriber units 14 based on a Time Division Multiplexingscheme. Specifically, a forward link traffic, channel 42 is optionallypartitioned into a predetermined number of periodically repeating timeslots for transmission of data packets from the base station 20 tomultiple subscriber units 14. It should be understood that a givensubscriber unit 14 can, at any instant in time, have multiple time slotsor no time slots assigned to it for use. In certain applications, anentire time-slotted forward or reverse link traffic channel can also beassigned for use by a particular field unit 14 on a continuous basis.

[0049]FIG. 2 is a timing diagram illustrating multiple channels on whichmessages are transmitted between a base station 20 and field units 14according to certain principles of the present invention. As shown,field units 14 can transmit messages to base station 20 over a dedicatedchannel such as access channel 51. Access channel 51 supports atransmission of access request messages from a field unit 14 to basestation 20. An access request message can indicate a request by fieldunit 14 for a high speed bi-directional communication link.

[0050] Message transmissions over access channel 51 need not be limitedto access request type messages. For example, access channel 51 can bestructured to support other types of messages.

[0051] In the illustrative timing diagram as shown in FIG. 2, accesschannel 51 is optionally partitioned into periodically repeating timeslots 210 in which messages are transmitted from a field unit 14 to basestation 20. More specifically, an Epoch on the order of 26.6 mS induration can be partitioned to include time slot #0 and time slot #1 asshown. In this application, a field unit or multiple field units 14 canrandomly send messages to base station 20 in either time slot of anEpoch. Providing multiple time slots 210 in which a field unit 20 cantransmit a message renders it less likely that two randomly transmittingfield units 14 will transmit a message in a same time slot 210.Depending on an application, a field unit 14 can be synchronized withbase station 20 using pilot channel 44 so that messages can betransmitted in a particular time slot 210.

[0052] When a collision occurs, i.e., two field units 14 transmit amessage in the same time slot 210, a device monitoring access channel 51for such messages may not be able to properly decode or decipher thecontent of either transmitted message. An indication of this conditionis transmitted to field units 14.

[0053] Feedback channel 45 is provided so that base station 20 can sendfeedback messages 230 to field units 14. At least a portion of thefeedback channel 45 as shown is reserved for transmitting generalmessages to the collective field units 14 whether or not a messagecollision occurred on access channel 51 in a previous Epoch and, moreparticularly, that a message occurred in a particular time slot 210.

[0054] A feedback message 230 is optionally a sequence of encodedinformation or single bit indicating whether a collision occurred for amessage transmitted to base station 20 in a time slot 210. As shown,multiple feedback messages 230 can be generated during a given timeduration such as an Epoch or half Epoch. For example, feedbackinformation such as feedback messages 230 can be transmitted in durationA of Epoch N+1 to indicate that a collision occurred for the receptionof a message 210 in time slot #0 of Epoch N at base station 20. Morespecifically, a logic 1 transmitted in each of three feedback messages230 of duration A can indicate that a collision was detected while alogic 0 setting can indicate that no collision was detected.

[0055] Transmitting multiple, spaced feedback messages 230 as shown forduration A provides redundancy to some extent. For example, multiplemessages 230 transmitted in a given duration, such as duration A, can bepart of a redundantly transmitted message to increase the chance that afield unit 14 will be properly notified whether a collision occurs.Hopefully, at least one of the multiple feedback messages 230 can beidentified at a field unit 14 even if a message transmission failureoccurs for some of the messages 230 in, for example, duration A.

[0056] In a similar manner as previously discussed, feedback messages230 of feedback channel 45 transmitted in duration B of Epoch N+1 canindicate whether a message collision is detected in time slot #1 ofEpoch N as monitored by base station 20.

[0057] In a reverse link direction, a message transmitted by a fieldunit 14 to base station 20 on access channel 51 includes uniqueinformation such as the identification number of the field unit 14transmitting the message. In forward link direction, paging channel 41supports message transmissions from base station 20 to field units 14,where the message transmissions are typically directed to a specificfield unit 14. Thus, base station 20 can respond to a field unit 14 thatsent a message on access channel 51 by transmitting a reply message tothe field unit 14 over paging channel 41. Other link informationforwarded on the paging channel 41 can be forwarded to a field unit 14to establish a formal bidirectional link between base station 20 andfield unit 14.

[0058] One type of message transmitted on paging channel 41 is an ACK(acknowledgment) message 240. ACK messages 240 are sent by base station20 to indicate that a message received in a time slot 210 of accesschannel 51 was properly received. Similar to the feedback messages 230on feedback channel 45, ACK messages transmitted to a field unit 14 arealso feedback messages. However, an ACK message 240 indicates that aprevious access request message transmitted by a field unit 14 wasproperly received. ACK message 240 can also indicate that a formalcommunication link will be established with the access requesting fieldunit 14. For instance, traffic channels can be assigned to field unit 14for transmitting or receiving a data payload.

[0059] It should be noted that field units 14 optionally transmit atsuch a low power output level that messages transmitted in a particulartime slot 210 are not detected at base station 20. In this instance, afield unit 14 can adjust its power output level for a subsequent messagetransmission based on feedback information received from base station20. More specifically, a field unit 14 can adjust its power output leveldepending on a feedback message 230 or ACK message 240 received onfeedback channel 45 or paging channel 41 respectively. Accordingly, thepower output level of a field unit 14 can be optimized so that itminimally interferes with other field units 14 transmitting informationover a common radio frequency.

[0060] Although other message types can be supported, the messagestransmitted in a time slot 210 of access channel 51 are typically accessrequest messages indicating that a field unit 14 would like to receiveor transmit data payload information on reverse link traffic channels 52or forward traffic channels 42.

[0061] One aspect of adjusting the power output of a field unit 14 is todetermine whether or not a collision was detected for a previous messagetransmission from the field unit 14 to base station 20. For example, ifa collision is not detected for a previously transmitted message from aparticular field unit 14, the power output level for a subsequentmessage transmission from the field unit 14, if any, can be increased sothat base station 20 is more likely to detect the message transmission.More specifically, the power output level of a field unit 14 can beincreased a predetermined amount such as +0.5 dB for a subsequentmessage transmission if no collision was detected for a previous messagetransmission.

[0062] In the event that a message transmission by a field unit 14 doesresult in a collision due to multiple field units 14 transmitting in asame time slot 210, the power output level of the field unit 14 can beunchanged or potentially reduced for a subsequent message transmissionsince it is not known whether the message transmission by a field unit14 would have otherwise been detected at base station 20 if only onefield unit 14 transmitted a message within a particular time slot 210.Hence, one aspect of the present invention involves adjusting the poweroutput level of a field unit 14 so that it minimally interferes withothers using the same radio channel.

[0063] This method of transmitting messages can be particularly usefulwhen a user first powers a field unit 14 and must communicate with basestation 20. For example, it is undesirable in certain situations totransmit a message at such a high power output level that such messagetransmissions cause other data transmissions on the radio channel tobecome corrupted due to excessive noise.

[0064] In a similar manner as previously discussed, the power outputlevel of a field unit 14 can be adjusted depending on whether basestation 20 acknowledges receipt of a message on access channel 51. Thus,if field unit 14 does not detect a reply ACK message 240, the poweroutput level of field unit 14 can be increased for subsequent messagetransmissions.

[0065] A maximum power adjustment level such as 60 dBm can be selectedin which the field unit 14 will discontinue transmitting if no ACKmessage is received even at this level.

[0066] A more sophisticated application of the present invention caninvolve adjusting a power output level of a field unit 14 depending onboth a feedback message 230 indicating whether a collision was detectedand an ACK message 240 indicating that an access message wasacknowledged by base station 20. More specifically, a field unit 14 canadjust its power output level for subsequent message transmissions if nocollision is detected and no ACK message is received for a previouslytransmitted message from a field unit 14. Otherwise, the field unit 14can re-transmit at a previous power output level.

[0067] Regardless of which method is used to adjust the power outputlevel, the power level setting at which base station 20 acknowledgesreceipt of a message from a field unit 14 can be used to determine powerlevel settings at which the field unit 14 must transmit otherinformation to base station 20. For example, a message from a field unit14 can be transmitted using a particular modulation rate during theinitial message transmission. The power output level of subsequenttransmissions from the field unit 14 can be adjusted to accommodatetransmitting messages at different modulation rates. For example, it canbe determined at what power level a field unit should transmit onallocated traffic channels using a different modulation rate. A historyof the power level output adjustments are optionally maintained to trackpower adjustments and determine at what power level a monitoring devicesuch as base station 20 detects the transmission of a message.

[0068] As previously discussed, one aspect of the present inventioninvolves re-transmitting a message from a field unit 14 so that it canbe detected at base station 20. A re-transmission is optionally based ona random back off time so that a collision is less likely to occur on asubsequent attempt to transmit a message.

[0069] Consider a situation where two or more field units 14 transmit amessage over access channel 51 and a collision is detected at basestation 20. As previously discussed, a feedback message will betransmitted to the field units 14 indicating that a collision occurred.Both field units 14 must then re-transmit their corresponding messagesto base station 20.

[0070] To avoid another collision, the field units 14 randomly choose aback off time relative to the previous message transmission in which thecollision occurred and transmit in another time slot 210. For example,if field unit A and field unit B transmit a message in time slot #0 ofEpoch N, field unit A will choose a back off time such as 3 Epochs andre-transmit a message to base station 20 in time slot #1 of Epoch N+3while field unit B re-transmits a message based on a random back offtime in time slot #0 of Epoch N+2. Accordingly, field units A and B areless likely to cause another collision for a message re-transmission.

[0071]FIG. 3 is a timing diagram illustrating another embodiment of thepresent invention for transmitting feedback messages to field units 14.An access channel 51 is partitioned so that a field unit 14 can transmitan access probe or other message in a time slot 345. As shown, feedbackchannel 355 is partitioned to include 64 time slots TS#0, TS#1, TS#2 . .. TS#63 that repeat every Epoch.

[0072] Each time slot 315 of feedback channel 355 preferably includes adata field supporting 16 bits of information. In the specificapplication as shown, ten bits of information are reserved for a generalmessage, one bit is reserved as a collision detect bit 325 and five bitsare reserved for CRC (Cyclical Redundancy Check) data 328. Generalmessage 320 is optionally a message directed to a particular field unit14. For example, each of multiple field units 14 can be assigned use ofa particular time slot 315 for receiving feedback information from basestation 20 to field units 14. When assigned, a corresponding field unit14 monitors an appropriate time slot 315 to receive messages from basestation 20. One type of specific message in a time slot 315 is feedbackinformation to a field unit 14 indicating how its timing or power shouldbe adjusted so that messages transmitted from a field unit 14 areproperly received at base station 20.

[0073] Time slots 315 are optionally unassigned and the message itselfcan include an address to which field unit 14 a message is directed.Thus, in a modified embodiment, feedback messages can be transmittedasynchronously to a field unit 14.

[0074] Collision detect bit 325 in a time slot 315 is a single bitindicating whether a collision occurred in a monitored time slot 345.More specifically, collision detect bits 325 of time slot TS#0, TS#1 . .. TS#31 of Epoch M can be used to indicate that a collision occurred inaccess probe slot #0 of Epoch M−1. Accordingly, this string ofindividual collision detect bits 328 over multiple time slots can be setto a same logic state indicating that a collision was detected.

[0075] In a similar manner, TS#32, TS#33 . . . TS#63 of Epoch M can beset appropriately to indicate whether a collision occurred on accessprobe slot #1 of Epoch M−1. Thus, a monitoring field unit 14 candetermine whether a collision occurred at base station 20 based on asingle bit, a sequence of multiple bits, or a sequence of spaced bits.

[0076] CRC data 328 is also provided in a feedback message 360. The CRCdata 328 is optionally decoded at the field unit 14 to ensure that amessage 360 is properly received at a field unit 14 and, morespecifically, that a particular collision detect bit 325 is properlyreceived. Other methods can also be used to ensure and verify that amessage and data is properly received at field unit 14. For example, amessage can be transmitted based on an FEC (Forward Error Correction)code.

[0077]FIG. 4 is a diagram illustrating a format for transmittingmessages over the access channel from a field unit to a target receiveraccording to the principles of the present invention.

[0078] In one application, message 410 is transmitted by a field unit 14over access channel 51 and includes two parts. As shown, a first part orpreamble 415 of message 410 is a coded message indicating a request bythe field unit 14 for a communication link. Each field unit 14 cantransmit a message 410 having a commonly coded preamble 415. Thus, iftwo field units 14 transmit a message including the same preamblemessage 415, base station 20 can determine that at least a preamblemessage 415 was sent by at least one field unit 14. That is, thepreamble message 415 as transmitted by one field unit can overlap withthe preamble message 415 as transmitted by another field unit 14 whenmultiple messages 410 are transmitted in the same time slot.

[0079] Message 410 optionally includes a data payload 420 that istransmitted to base station 20. In one application, data payload 420includes the serial number of the field unit 14 transmitting message410. Typically, some form of redundancy check information such as CRCdata is included with message 410 so that base station 20 can determinewhether message 410 is properly received without errors.

[0080] If message 410 is received without errors, base station 20 canrespond accordingly to establish a link with a field unit 14 andtransmit a “non-collision” message on feedback channel 45 to the fieldunits 14. Alternatively, if message 410 includes an error free preamble415 but improperly received data payload information 420, base station20 can deduce that two or more transmitters sent a message at the sametime. A collision detection message is then transmitted over feedbackchannel 45 indicating that a collision occurred. Thus, a target receiversuch as base station 20 monitoring messages 410 can provide valuablefeedback to multiple transmitting field units 14 whether a messagecollision occurs.

[0081] Another aspect of the present invention involves coding apreamble 415 using pilot block 53 and Barker code block 54. Based onthis coding or use of a sequence of symbols, a field unit 14 cantransmit a message 410 to base station 20.

[0082] As shown, a preamble message 415 can include four pilot blocks 53and four Barker code blocks 54. The Barker code blocks 54 assist basestation 20 identify a point where preamble 415 of a message 410 starts.In other words, the information in the preamble 415 can be used fortiming purposes at the base station 20 to asynchronously receive amessage. Thus, it is not necessary that a field unit 14 transmit amessage 410 in a time slot 210 because base station 20 can be modifiedto receive asynchronous messages.

[0083] However, in an application where messages 410 include Barker codeblocks 54 that are transmitted in a time slot 210, base station 20 canidentify a received message 410 even if a collision occurs because thepreamble 415 of a message 410 simultaneously transmitted by multiplefield units 14 in a time slot will overlap and, thus, will be detectableat base station 20.

[0084] Each pilot block 53 includes a number of repeating pilot symbols.Preferably, a pilot block includes 48 symbols that are used by a targetreceiver to decode message 410.

[0085] The second portion of a message 410 can include a data payload420 that is sent to base station 20. Preferably, pilot symbols are alsoinserted in the data payload 420 portion of message 410 for assisting incoherent demodulation of-data at a target receiver. Pilot symbolstypically include a series of positive data bits and therefore do notthemselves inherently include timing information.

[0086] A Barker code block 54 as shown includes a predetermined patternof bit information. Use of BPSK (Binary Phase Shift Keying) can be usedto generate a positive barker sequence 450, +B, such as three positivebits, followed by three negative bits, a positive bit, a pair ofnegative bits, a positive bit and then a negative bit respectively. ABarker code sequence can alternatively be negative such as a negativeBarker sequence, −B, further assisting in message processing at amonitoring device. Further details for processing message 410 includingpilot blocks 53 and Barker code blocks 54 can be found in co-pendingU.S. patent application Ser. No. 09/766,875 filed on Jan. 19, 2001entitled “Access Channel Structure for Wireless Communication System,”the entire teachings of which are incorporated herein by reference.

[0087]FIG. 5 is a flow chart illustrating a process for monitoring achannel for messages according to the principles of the presentinvention.

[0088] Step 500 generally indicates an entry point into the flow chart.In step 510, an access channel 51 is monitored for message transmissionssuch as access request messages transmitted by a field unit 14. It isthen determined in step 520 whether the message includes a Barker codeor an appropriately received preamble 415 of a message 410. If no Barkercode or preamble 415 is detected in step 520, process flow resumes atstep 510 again. Alternatively, if a Barker code is detected in step 520,the message 410 is further analyzed to determine if a collision occursin a time slot. That is, it is determined whether at least a portion ofdata in a received message 410 is corrupted.

[0089] One way to determine if a message collision occurs is to verifythat data in a message 410 was properly received. This can be achievedby analyzing the received message 410 according to redundancy checkinformation. If the data in a message 410 is not properly received atbase station 20, a feedback message is transmitted by base station 20over feedback channel 45 indicating that a collision was detected for aprevious access request message in step 540. Following step 540, processflow resumes again at step 510.

[0090] If a collision is not detected for a particular message in step530, the message 410 is analyzed to determine which of multiple fieldunits 14 sent the message. Following in step 550, an ACK message 240 issent to the requesting field unit 14 over the paging channel 41. Also, amessage is sent over the feedback channel 45 indicating that no messagecollision occurred for the corresponding previous time slot 210 ofaccess channel 51. Finally, a more formal link is established with theaccess requesting field unit in step 560.

[0091]FIG. 6 is a flow chart illustrating a process flow at a field unitfor transmitting a message to a target receiver according to theprinciples of the present invention. Step 600 generally indicates anentry point into the flow chart.

[0092] In step 620, the status of field unit 14 is monitored for aninput by a user indicating that the field unit 14 desires to establish acommunication link with a target receiver such as base station 20. It isthen determined in step 620 whether the input indicates that a fieldunit 14 desires to establish a communication link. If not, process flowagain resumes at step 610. If so, field unit 14 transmits an accessrequest message on the access channel 51 in step 630. Thereafter, thefeedback channel 45 is monitored by a field unit 14 in step 640 forfeedback information such as collision detection messages.

[0093] If a collision is detected for a previous transmission by a fieldunit 14 in step 650, process flow continues at step 660 where the poweroutput level is not adjusted for the field unit 14 and a message 410 issubsequently re-transmitted in step 630. If a collision is not detectedin step 650 as indicated by a collision feedback message, it isdetermined in step 670 whether an ACK message 240 is received at thefield unit 14 over paging channel 41. If so, a link is establishedbetween the field unit 14 and base station 20 in step 690. If not, thepower output level of the field unit 14 is increased in step 680 andprocess flow continues at step 630 to re-transmit a message from thefield unit 14 to base station 20.

[0094]FIG. 7 is a timing diagram illustrating multiple channels on whichmessages are transmitted among transceivers according to the principlesof the present invention.

[0095] As previously discussed, one aspect of the present inventioninvolves setting a field unit 14 to an initial power level so that itminimally interferes with other users during a message transmission.Since power is ramped up based on whether an access message is detectedat base station 20, it is preferable that the initial power level of thefield unit is reasonably near a power level at which base station 20will receive a message at a desired power level. Consequently, a fieldunit 14 will be able to transmit a message to base station 20 andestablish a more formal communication link in less time since a powerlevel output of field unit 14 will need only minimal adjustments so thata message is received at base station 20.

[0096] One method for initially setting a power output level of a fieldunit 14 involves transmitting a reference signal 710 on pilot channel 44from base station 20. Preferably, the reference signal 710 istransmitted at an appropriate power level so that multiple field units14 in a wireless airspace monitoring the pilot channel 44 can identifythe reference signal 710 and measure a power level at which it isreceived. In one application, reference signal includes pilotinformation such as a sequence of pilot symbols, where the pilot symbolsare defined by PN (Pseudo Noise) codes. One or multiple pilotcorrelation filters in field unit 14 is used to detect the pilotsymbols.

[0097] Each field unit 14 monitoring the pilot channel 44 typicallyincludes a power detector circuit to measure a power level of thereceived reference signal 710. For example, the power detector is usedto measure the strongest pilot path of the received reference signal710. This measurement is used to estimate a forward path loss betweenbase station 20 and field unit 14.

[0098] The total received signal power level of the reference signal 710can be computed based on the sum of the magnitude squared of the I and Qchannel. Power measurements are optionally filtered for providing abetter estimate of a received power level under fading conditions.

[0099] As shown in FIG. 7, messages are transmitted on paging channel 41from base station 20 to field units 14. One such message is message Athat includes information indicating a power level at which referencesignal 710 is transmitted from base station 20. This value can beexpressed in dBm that already takes into account the gain of the basestation antenna. Thus, message A can include effective radiated powerlevel information at which base station 20 transmits reference signal710. In harmony with the principles of the present invention, additionalmessages such as antenna gain information, offset information,correction information and general information can be transmitted to afield unit 14.

[0100] Field unit 14 decodes message A to determine a power level atwhich reference signal 710 is transmitted. The forward path loss betweenbase station 20 and field unit 14 is then determined by comparing thereceived power level of the reference signal 710 at field unit 14 withthe effective radiated power level as indicated by message A.

[0101] The calculated forward path loss can then be used to estimate areverse path loss between field unit 14 and base station 20. Forexample, the reverse path loss is estimated to be about the same as theforward path loss, although it is probably at least slightly different.This estimated path loss is used to determine an initial setpoint atwhich messages can be transmitted from field unit 14 to base station 20.

[0102] Consider a case where base station 20 transmits a referencesignal 710 at an effective radiated power level of 55 dBm. As discussed,this information is sent to field units 14 via message A generallybroadcasted on the paging channel 41. If the received power level of thereference signal 710 is 22 dBm, the forward path loss is calculated as55−22 dBm, or forward path loss=33 dBm. Based on this path loss, a fieldunit 14 can estimate a reasonable power output level for a subsequentattempt to transmit a message to base station 20.

[0103] Additional messages can be sent on paging channel 41 from basestation 20 to field units 14. For example, message B is also generallytransmitted to field units over paging channel 41. Message B preferablyincludes encoded information indicating a desired power level at whichbase station 20 will receive subsequent messages from a field unit 14.This information can also be a specific message directed transmitted toa particular field unit 14. Thus, a field unit 14 can use theinformation to estimate at what level a message should be transmitted sothat a message is received at the desired power level. In a case wheremessage B indicates a desired power level of 12 dBm and the forward pathloss is approximately 33 dB as discussed, field unit 14 can attempt totransmit a message at 33+12 dBm, or 45 dBm, to base station 20.

[0104] Notably, the reverse path loss may be much more than 33 dBm asestimated. In such a situation, base station would not necessarilydetect a message transmitted by field unit 14. As previously discussed,however, the power output setpoint of 45 dBm can be a starting point atwhich messages such as access request messages 750 are transmitted overaccess channel 51. If a collision is not detected at base station 20 andno ACK message 240 is received over paging channel 41, the power outputof field unit 14 can be increased by 1 dBm to 46 dBm for a subsequentattempt to transmit a message. This procedure of adjusting the poweroutput level of a field unit 14 can be repeated until a message isdetected at base station 20.

[0105] Messages transmitted to base station 20 can also be monitored todetermine a power level at which a message is received from a field unit14. To achieve this end, a message such as message C can include pilotinformation such as a pilot symbol or sequence of pilot symbols. Pilotcorrelation filters are then used to identify the strongest diversitypath and side paths as shown in FIG. 8. One or multiple paths are thenused to determine a power level at which the message is received at basestation 20 on access channel 51. To ensure that a message C is properlyreceived, the message is analyzed for errors using error detectioninformation such as CRC check bits. These and other aspects of inventionwere previously discussed in this specification.

[0106] After message C is properly received at base station 20, a poweradjustment message is generated at base station 20 to indicate how thefield unit 14 should be adjusted so that subsequent messages to basestation 20 are received at a desired power level. For example, if basestation 20 determines that a message is received at 23 dBm, base station20 can send a message over paging channel 41 indicating that the fieldunit should reduce its power output level for subsequent messagetransmissions so that a message from a field unit is received at a lowerpower level such as 12 dBm.

[0107]FIG. 8 is a graph illustrating a received diversity string for apilot symbol according to the principles of the present invention. Areceived message such as reference signal 710, message A, message B ormessage C can include a marker such as one or multiple pilot symbolsthat are monitored at a receiver to determine a power level of areceived message.

[0108] Both base station 20 and field units 14 include pilot correlationfilters for identifying a marker such as one or multiple pilot symbolsin a transmitted message. This marker aids in analyzing both timingalignment and a received power level of a message. Incidentally, thediversity string illustrates the receipt of a marker in a message as aresult of multipath fading. That is, a signal from a transmitter isreceived at a target at different times due to varying times it takesfor the signal to reach the target over different paths between atransmitter and receiver.

[0109] Preferably, the strongest received diversity path will bedesignated as the time alignment string at base station 20 field unit 14for analyzing the timing of a received message. Likewise, the singlestrongest path is preferably chosen to calculate a power level at whicha message is received. However, additional paths are optionally used todetermine a received power level of a message.

[0110] Timing alignment and a received power level of a message isdetermined using the correlation profile of the strongest pilot in aparticular string, which is analyzed as mentioned using correlationfilters. The output of the correlation filters typically consist of 256samples, which represent 64 lags at 4 samples per lag. The 256 sampleoutput-window represents the total correlation time span of a receiverdevice. This can vary depending on the application. Preferably, the timealignment point is sample number 80 which allows 20 lags for precursorand 44 lags for post cursor channel information.

[0111] Generally, the computation of the time alignment error is basedon a determination of where the centroid or peak lies in a given samplestring. For example, each field unit 14 transmitting in a time slotincludes a marker, i.e., the peak signal, located at a predeterminedposition within a time slot. The strongest pilot path for the channeland 2 samples on either side of the main path, i.e., 1 and ¼ chips, isstatistically analyzed to determine the centroid or peak of a markerwithin a time slot. Location of the centroid, L, of the samples in FIG.6 is calculated based on the following equation:$L = \frac{\sum\lbrack {t\quad x\quad {Q( + )}} \rbrack}{\sum{Q(t)}}$

[0112] where t=sample time and Q(t) is the magnitude of a sample at agiven time. For example, L is calculated based on the results as shownin FIG. 6: $\begin{matrix}{L = \frac{( {{.25}*76} ) + ( {{.5}*77} ) + ( {1.0*78} ) + ( {{.8}*79} ) + ( {{.6}*80} )}{{.25} + {.5} + 1.0 + {.8} + {.6}}} \\{{L = 78.317}\quad}\end{matrix}$

[0113] Again, the timing alignment error is determined by comparing thetiming of the computed centroid to the desired time set point of 80,which is chosen as the reference point for timing alignment within atime slot. Since the centroid in the example above is estimated to be78.317, timing is early relative to the set point of 80. An appropriatemessage can be sent to field unit 14 indicating how its timing should befinely tuned so that messages from field unit 14 are received at theappropriate time at base station 20. In a similar manner, the diversitystring of FIG. 8 can be analyzed to determine a power level at which amessage is received. Thus, an appropriate message can be sent to fieldunit 14 indicating how its power output level should be adjusted so thata message is received at a desired power level.

[0114] As mentioned, this technique can be used to detect a receivedpower level of reference signal 710 at base station 20.

[0115] More details regarding timing alignment and power control betweena base station 20 and each of multiple field units 14 can be found inco-pending U.S. Application No. (2479.1067-001) entitled “MinimalMaintenance Link to Support Synchronization” filed on Feb. 7, 2001, andco-pending U.S. application Ser. No. 09/775,305 entitled “MaintenanceLink Using Active/Standby Request Channels” filed on Feb. 1, 2001, theentire teachings of both of which are incorporated herein by reference.

[0116]FIG. 9 is a flow chart illustrating a method for setting a powerlevel output of a field unit based on an estimated path loss accordingto the principles of the present invention.

[0117] Step 900 indicates an entry point into the flow chart. Followingin step 910, field unit 14 monitors pilot channel 44 for referencesignals 710. As previously discussed, the field unit determines a powerlevel at which reference signals 710 are received using a power detectorcircuit and pilot correlation filters.

[0118] In step 920, paging channel 41 is monitored by a field unit 14for messages transmitted from base station 20. As previously discussed,message A is received on paging channel 41 and decoded to determine aneffective radiated power level at which reference signals 710 are beingtransmitted from base station 20.

[0119] Based on the detected power level of reference signal 710 asreceived at field unit 14 and corresponding effective radiated powerlevel at which the reference signal 710 is transmitted from base station20, a path loss is estimated between the base station and field unit 14in step 930. Preferably, the path loss is estimated by computing thedifference between the power level at which reference signal 710 istransmitted from base station 20 and a power level at which referencesignal 710 is received at field unit 14.

[0120] Message B is subsequently received at field unit 14 in step 940.This message preferably includes information indicating a desired powerlevel at which messages are to be received at base station 20.

[0121] Based on the desired power level at which messages are to bereceived at base station 20 and the estimated path loss in step 930,field unit 14 determines a power output setting for field unit 14 sothat a message is received at the desired power level at base station 20in step 950. More specifically, it is presumed that an actual path lossfrom the field unit 14 to base station is approximately the same as thecalculated path loss between the base station and field unit 14 based onmeasurements of reference signal 710. Thus, an appropriate power outputlevel of field unit 14 can be determined by adding the estimated pathloss to the desired power level setting to determine a power outputsetting for field unit 14. Consequently, this power output setting of afield unit 14 should be a reasonable starting point for attempting totransmit an initial message to base station 20.

[0122] Also in step 950, field unit 14 transmits message C such as anaccess request message to base station 20 over access channel 51. Uponreceipt, base station 20 measures a received power level of message C atbase station 20. This received power level is then compared to thedesired power level so that feedback can be provided to field unit 14indicating how to adjust its power output level so that subsequentmessages are received at the desired power level.

[0123] Following in step 960, field unit 14 monitors paging channel 41for an ACK message indicating that base station 20 properly receivedmessage C. If an ACK is not received in step 970, the power output levelof a field unit 14 is increased in step 975 and the message issubsequently re-transmitted in step 960. This loop of increasing powergenerally repeats until base station 20 acknowledges receipt of themessage.

[0124] When an ACK is received in step 970, process flow continues atstep 980 in which additional messages are received from base station 20indicating whether the message transmitted in step 950 was received atthe desired power level. As discussed, information can be transmitted toa field unit 14 indicating how to adjust its power output level so thatsubsequent messages are received at the desired power level at basestation 20. Consequently, the output power level of the field unit 14 isadjusted accordingly for subsequent message transmissions.

[0125] While this invention has been particularly shown and describedwith references to preferred embodiments thereof, it will be understoodby those skilled in the art that various changes in form and details maybe made therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A method for supporting wireless communications,the method comprising the steps of: detecting that a collision occurs ata first transceiver when two or more second transceivers attempt to sendmessages over a first channel, a collision occurring when each of thetwo or more second transceivers transmit messages on the first channel,at least a portion of each message transmitted in a time slot overlap, acommon encoded sequence of the messages being detectable at atransceiver even though there is a collision; notifying the two or moresecond transceivers of a collision on the first channel by sending amessage from the first transceiver to the two or more secondtransceivers over a feedback channel; adjusting a power output level ofa corresponding one of the two or more second transceivers attempting tosend a message over the first channel depending on whether a collisionoccurs on the first channel, the step of adjusting further comprising:transmitting a first message from the first transceiver, the firstmessage including effective radiated power level information at whichthe first transceiver transmits a reference signal; measuring a receivedpower level of the reference signal received at the corresponding secondtransceiver; decoding the first message at the second transceiver todetermine the effective radiated power level information; and estimatinga path loss between the first and second transceivers by comparing thereceived power level and the effective radiated power level information.2. A method as in claim 1 further comprising the step of: transmitting asecond message from the first transceiver to the second transceiverindicating a desired power level at which subsequent messages shall bereceived at the first transceiver.
 3. A method as in claim 2 furthercomprising the step of: transmitting a reply message from the secondtransceiver to the first transceiver at a power level so that the firsttransceiver receives the reply message at the desired power level.
 4. Amethod as in claim 2 further comprising the step of: determining a poweroutput setting at the second transceiver based on an estimated path lossso that a message is received at the first transceiver at the desiredpower level.
 5. A method as in claim 1, wherein the first message istransmitted over a paging channel of a CDMA (Code Division MultipleAccess) communication system.
 6. A method as in claim 3, wherein thereply message is transmitted over an access channel of a CDMAcommunication system.
 7. A method as in claim 1, wherein the secondtransceiver transmits an access request message to the first transceiverin a time slot of an allocated reverse channel.
 8. A method as in claim7, wherein the access request message from the second transceiver to thefirst transceiver includes encoded information for measuring timingalignment of the second transceiver.
 9. A method as in claim 1, whereinthe second transceiver, a mobile transceiver, sends a reply message tothe first transceiver, a base station transceiver, the reply messageincluding a reference marker that is monitored for generating feedbackmessages to synchronize the mobile transceiver to the base stationtransceiver.
 10. A method as in claim 1, wherein the first transceivertransmits the first message over a dedicated channel to multipletransceivers.
 11. A method as in claim 1 further comprising the step of:measuring a power level at which a reply message transmitted from thesecond transceiver is received at the first transceiver.
 12. A method inclaim 11 further comprising the steps of: comparing a power level atwhich the reply message is received at the first transceiver with adesired power level at which messages should be received; andtransmitting a power adjustment message to the second transceiver forsubsequent message transmissions.
 13. A method as in claim 1, whereinthe reference signal includes pilot symbols.
 14. A method as in claim 1,wherein the reference signal is transmitted over a pilot channel.
 15. Amethod as in claim 1, wherein a path loss is calculated based on thedifference between an effective radiated power level of the referencesignal and power level of one or multiple received reference signals.16. A method for supporting wireless communications, the methodcomprising the steps of: detecting that a collision occurs at a firsttransceiver when two or more second transceivers attempt to sendmessages over a first channel, a collision occurring when each of thetwo or more second transceivers transmit messages on the first channel,at least a portion of each message transmitted in a time slot overlap, acommon encoded sequence of the messages being detectable at atransceiver even though there is a collision; notifying the two or moresecond transceivers of a collision on the first channel by sending amessage from the first transceiver to the two or more secondtransceivers over a feedback channel; adjusting a power output level ofa corresponding one of the two or more second transceivers attempting tosend a message over the first channel depending on whether a collisionoccurs on the first channel, the step of adjusting further comprising:transmitting a first message from the first transceiver, the firstmessage including power level information at which the first transceivertransmits a reference signal; measuring a received power level of thereference signal received at the corresponding second transceiver;decoding the first message at the second transceiver to determine theeffective radiated power level information; estimating a path lossbetween the first and second transceivers by comparing the receivedpower level and the effective radiated power level information;measuring a power level at which a reply message transmitted from thesecond transceiver is received at the first transceiver; and providingfeedback information to the second transceiver how to adjust its poweroutput level.
 17. A method in claim 16 further comprising the steps of:comparing a power level at which the reply message is received at thefirst transceiver with a desired power level at which messages should bereceived; and transmitting a power adjustment message to the secondtransceiver for subsequent message transmissions.
 18. A method in claim1 further comprising the step of: transmitting a second message from thefirst transceiver to the second transceiver indicating a desired powerlevel at which subsequent messages shall be received at the firsttransceiver.
 19. A method in claim 18 further comprising the step of:transmitting a reply message from the second transceiver to the firsttransceiver at a power level so that the first transceiver receives thereply message at the desired power level.
 20. A method as in claim 18further comprising the step of: determining a power output setting atthe second transceiver based on an estimated path loss so that a messageis received at the first transceiver at the desired power level.
 21. Amethod as in claim 16, wherein the first message is transmitted over apaging channel of a CDMA (Code Division Multiple Access) communicationsystem.
 22. A method as in claim 19, wherein the reply message istransmitted over an access channel of a CDMA communication system.
 23. Amethod as in claim 16, wherein the second transceiver transmits anaccess request message to the first transceiver in a time slot of anallocated reverse channel.
 24. A method as in claim 23, wherein theaccess request message from the second transceiver to the firsttransceiver includes encoded information for measuring timing alignmentof the second transceiver.
 25. A method as in claim 16, wherein thesecond transceiver sends a reply message to the first transceiver, thereply message including a reference marker that is monitored for timingalignment.
 26. A method as in claim 16, wherein the first transceivertransmits the first message over a dedicated channel to multipletransceivers.
 27. A method as in claim 16, wherein the, reference signalincludes pilot symbols.
 28. A method as in claim 16, wherein thereference signal is transmitted over a pilot channel.
 29. A method as inclaim 16, wherein a path loss is calculated based on the differencebetween an effective radiated power level of the reference signal andpower level of one or multiple received reference signals.